[OT] x86 assembler question

Hi all,
I hate to do this, but I've posted to lots of forums and found no answer.
I'm doing some research on dongle software protection, and one site referred
to response codes being 'impossible to recover because you'll sometimes end up
with TEST [ESI+38],1 as a check.'
My asm is a bit rusty, but isn't this just an AND operation with a memory
location found in ESI plus an offset of 38? What's so hard about that?
Jonathon McKitrick
--
Hoppiness is a good beer.